<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
        <style>
            * {
                margin: 0;
                padding: 0;
            }
            a {
                color: black;
                size: 15px;
                text-decoration: none;
            }
            li {
                list-style: none;
            }

            #box {
                position: absolute;
                width: 110px;
                height: auto;
                margin: 50px 50px;
                /*border:1px solid red;*/
                /*z-index: 1;*/
            }
            #box .menu {
                    position: relative;
                    width: 110px;
                    /*border:1px solid blue;*/
                    /*z-index: 1;*/
            }
            #box .menu ul li {
                height: 33px;
                line-height: 33px;
                z-index: 1;
            }
            #box .menu ul li:hover {
                border:2px solid red;
                border-right:white ;
                /*z-index: 1;*/
            }
            #box .menu ul li a:hover {
                color: red;
            }
            #box .main
            {
                position: absolute;
                width: 400px;
                height: 300px;
                border:2px solid red;
                left: 110px;
                top: 0px;
                display: none;
            }
            #box .main ul {
                z-index: 1;
            }
            #box .main ul li {
                float: left;
                margin-left: 10px;

            }
            #box .main ul li.main_link {
                border: none;
            }
            #box:hover .main {
                display: block;
            }

        </style>

</head>
<body>
        <div id="box">
            <div class="menu">
                <ul>
                    <li> <a href="#">图书童书</a></li>
                    <li> <a href="#">图书童书</a></li>
                    <li> <a href="#">图书童书</a></li>
                    <li> <a href="#">图书童书</a></li>
                    <li> <a href="#">图书童书</a></li>
                    <li> <a href="#">图书童书</a></li>
                </ul>

                <div class="main">
                    <ul>
                        <li class="main_link"> <a href="#">图书童书</a></li>
                        <li class="main_link"> <a href="#">图书童书</a></li>
                        <li class="main_link"> <a href="#">图书童书</a></li>
                        <li class="main_link"> <a href="#">图书童书</a></li>
                        <li class="main_link"> <a href="#">图书童书</a></li>
                    </ul>
                </div>
            </div>
        </div>


</body>
</html>